Plant mitogen-activated protein kinases (MAPK) are involved in important processes, including stress signaling and development. MAPK kinases (MAPKK, MKK) have been investigated in several plant species including Arabidopsis thaliana, Oryza sativa, Populus trichocarpa, and Brachypodium distachyon. In the present study, nine putative maize MKK genes have been identified. Analysis of the conserved protein motifs, exon-intron junctions and intron phase has revealed high levels of conservation within the phylogenetic groups. Next, we defined four new ZmMKK-ZmMPK interactions using yeast two-hybrid. Finally, we examined the biological functions of the ZmMKK4 gene. Overexpression of ZmMKK4 in Arabidopsis conferred tolerance to oxidative stress by increased germination rate and early seedling growth compared with WT plants. Taken together, we provide a comprehensive bioinformatics analysis of the MKK gene family in maize genome and our data provide an important foundation for further functional study of MAPK and MKK families in maize. (C) 2013 Elsevier Inc. All rights reserved.